The present invention relates generally to carrier heads for chemical mechanical polishing.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. During polishing, the carrier head brings the exposed surface of the substrate into contact with a rotating polishing pad. The polishing pad may be either a “standard” or a fixed-abrasive pad. A standard polishing pad has durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad.
Some carrier heads include a flexible membrane with an inner surface that that encloses a chamber and an outer surface that provides a substrate mounting surface. By controlling the pressure in the chamber, the load applied to the substrate can be varied.
Another consideration in chemical mechanical polishing is the ability to detect the presence of the substrate in the carrier head. One problem that has been encountered in chemical mechanical polishing is that the attachment of the substrate to the carrier head may fail, and the substrate may detach from the carrier head. If this occurs, the operator may not be able to visually observe that the carrier head no longer carries the substrate. In this situation, a CMP apparatus will continue to operate even though the substrate is not longer being polished. This wastes time and decreases throughput. In addition, a loose substrate, i.e., one not attached to a carrier head, may be knocked about by the moving components of the CMP apparatus, potentially damaging the CMP apparatus itself or leaving debris which may damage other substrates.